Fail-safe mechanical timer

ABSTRACT

A fail-safe mechanical timer is provided having the speed retarding timing mechanism in series between the input power source and the timer output shaft.

United'States Patent Blitz 1451 July 18, 1972 [541 FAIL-SAFE MECHANICAL TIMER [56] Reierencee' emu [72] Inventor: DmielBlitz, Boston, Mass. UNITEDSTATES PATENTS Assigneer iand es, in, Nashua, NH. 3,446,007 5/1969 Cohen ..74/1.5 x 1 3,376,754 4/1968 066k ..74/1.5 [22] 'i 3,184,981 5/1965 Bennett etal ..74/142 211 Appl.N0.: 61,958 1,339,934 5/1920 Lindstrom .1ss/ o1o.1

. Primary ExdminerMilton Kaufman 52 us. c1. ..74/112,5s/116,74/1.s, Y

I v 2 I 74/142 Anot'ney Lou s Etllnger I 511 mu! 16h27/04 m 5s Fieldofselrch ..74/1.5,l42,1l2;58/ll6,23TF, [57] A CT 58/23 D; 102/84; l85/DIG. l

1 A fail-safe mechanieal timei is provided having the speed 1etarding timing mechanism in series between the input power source and the timer output shaft. 4

' Bow an-1111mm mama] Jun 8 m2 SHEEI10F4 {IO l2 |4 INPUT TIMER SPEED POWER OUTPUT RETARDING SOURCE SHAFT MECHANISM -,|4 SPEED RETARDING MECHANISM 1'0 FIG IE3 POWER SOURCE TIMER OUTPUT SHAFT 1o Y |4 l2 v lNPUT SPEED TIMER POWER RETARDING OUTPUT SOURCE MECHANISM SHAFT v INVENTOR. DANIEL BL 1 T2 ATTORNEY PmNIm-Juuamz 3371.101 sum 2 or 4 I INVENTOR. DAN l E L B L IT Z A T TORNE Y PATENTED JUL18I972 3 577 101 SHEET 3 OF 4 INVENTOR. DANIEL BLITZ PATENTEI] JUL 1 8 1912 3.677; 101

I sum u 0F 4 IINVENTOR.

DANIEL BLITZ I A TTORNE Y FAIL-SAFE MECHANICAL TIMER BACKGROUND OF THE INVENTION In many fuze armed systems, a mechanical timer is provided to insure that the arming is not completed until the device to be armed has traveled a safe distance from the launch site.

The timing mechanism generally includes gear trains which are driven by a spring. The speed of rotation of the gear trains is generally retarded by some type of mechanism, such as an escapement, to provide the desired delay time. Prior timing mechanisms have the output shaft driven directly by the spring input power source, with the retarding escapement driven either in parallel with the output, or else in series through the output. In either the series or parallel arrangements, defects in the escapement train manifested by, for example, broken gear shafts, gears with stripped teeth, gears which are misaligned, and therefore not meshing properly, or by some defect of the escapement mechanism, would disconnect the escapement speed retarding mechanism and allow the input power source to rotate the timer output shaft at high speed causing the timer to function early. Early timer functioning can be disastrous because premature arming of the fuze could occur immediately upon launch.

The prior art has attempted to prevent such failures from causing early functioning by sensing excessive speed malfunction and precluding arming by causing cessation of the 1 input power source and the speed retarding mechanism, and

mechanism. These malfunction sensing and mechanism stopping devices are relatively complex and subject to failure themselves, thereby only partially remedying the problem at hand.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a truly fail-safe mechanical timer.

It is another object of this invention to provide a mechanical timer that cannot speed up as a result of damage, but can only slow down or stop.

It is a further object of this invention to provide a timer to prevent premature detonation, of, for example, a bomb, despite any damage to the timer mechanism resulting from shock, fire, or other action.

Briefly, a fail-safe mechanical timer is provided wherein the speed retarding mechanism is placed in series between the power source and the timer output shaft such that any failure which disconnects the speed retarding mechanism also 'removes the connection between the power source and the timer output shaft, causing the output shaft to stop.

BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 18 represent block diagram formats of conventional mechanical timers, and FIG. 1C represents applicants mechanical timer;

FIG. 2 is a sketch of a simplified conventional mechanical- DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. IA and 18 set forth, conceptually, conventional mechanical timers whereby an input power source 10 drives directly a timer output shaft 12. The speed of the timer output shaft 12 is restrained by a speed retarding mechanism 14. FIG.

FIG. 1B shows the timer output shaft and the speed retarding mechanism connected in parallel to the input power source. As will be readily apparent from viewing these two conceptual block diagrams, any failure which disconnects the speed retarding mechanism allows the input power source to drive the timer output shaft at high speed, thereby causing premature operation of the timer, which in arming, for example, a missile or bomb, could be disastrous.

FIG. 1C illustrates, conceptually, applicant's new fail-safe mechanical timer wherein the speed retarding mechanism 14 is placed in series between the input power source 10 and the timer output shaft 12. In this arrangement, any failure of the speed retarding mechanism which disconnects it, though allowing the power source to run at high speed, will disconnect the timer output shaft from the energy supplied by the input power source, causing the output shaft to stop, thereby precluding premature arming.

A conventional simplified timer is illustrated in FIG. 2. This conventional timer comprises an input power source 16, including a shaft 36, which is rotated by the unwinding of a coil spring 20. The rotation of shaft 36 causes rotation of gears 18, 22, 24 and 26 in the directions shown. Gear 26 is arranged on a shaft 28 also having arranged thereon an escape wheel 30. An escapement fork 32 pivoted at point 34 cooperates with escape wheel 30 to retard the speed of the drive train. The timer output shaft for a series arrangement is located at 36. The spring input source 20 drives the output shaft 36, which in turn rotates gear 18 to drive the rest of the escapement train 22, 24, 26, 28, 30 and 32. Any defect in the escapement train, such as broken gear shafts, gears with stripped teeth, gears which are misaligned and not meshing properly, or other such damage, removes the speed restraint from the output shaft 36, allowing it to rotate at very high speed and cause premature functioning. The same failure results from an escapement train defect if the timer output shaft is arranged on a parallel gear train (not shown) as, for example, driven by gear 18.

FIG. 3 illustrates one simplified embodiment of a fail-safe mechanical timer. Input power is supplied to the timer by a spring powered gear 38. Gear 38 drives a gear 40, which is fixed to gear 41, which, in turn, drives a gear 42. Although only four gears, 38, 40, 41 and 42, are illustrated as the gear train in this particular embodiment, this is illustrative only and set forth for simplicity purposes. In actuality, the gear train may be made up of any number of gears. An escape wheel 44 is arranged on the same shaft, shaft 62, as is gear 42. Cooperating with escape wheel 44 is an escapement fork 46, pivoted at point 47 and having pallets 48 and 50 cooperating with the teeth of the escape wheel 44 to cause the escape wheel to move one tooth for each complete cycle of oscillation of fork 46. A pawl 52, mounted by pivot 51 on escapement fork 46 oscillates with the escapement fork 46. The

oscillation of pawl 52 pushes a ratchet wheel 54 in the direction shown, causing rotation of gear 56, which drives a gear 58, having a timer output shaft 60 thereon. A spring 59 holds the pawl 52 in contact with the teeth of ratchet wheel 54. A holdback pawl 53 pivoted at 55 and held against ratchet wheel 54 by a spring 57 can be used to prevent ratchet wheel 54 from rotating backward, if desired. Note again that gears 56 and 58 are only illustrative of a gear train, and any number of gears may be provided, as desired. The output shaft can be used, for example, to actuate an electrical switch or a mechanical latch.

In this embodiment, the speed retarding escapement mechanism is situated intermediate the power supply, spring powered gear 38, and the timer output shaft 60. Any catastrophic event disconnecting the speed retarding escapement, which would ordinarily cause the timer to race at high speed, will cause the escapement fork 46 to stop oscillating and thereby stop rotation of the output timer shaft 60. In effect, the oscillation of the escapement fork is used to run or power the train of gears to give an output. When it ceases, so does the output.

The previously described embodiment of the invention employs a runaway" escapement as the speed retarding mechanism. For many applications, runaway escapements have sufficient timing accuracy and provide sufficiently long time delays. However, if greater timing accuracy is desired, then a tuned escapement speed control can be employed. This is illustrated in FIG. 4.

The input power to the embodiment of FIG. 4 is applied to an input shaft 210 by, for example, a spring powered gear and gear train (not shown). Also arranged on shaft 210 is an escape wheel 212. The pallet teeth 214 and 216 of a pallet 218 cooperate with the escape wheel 212. An escapement spring 220 is inserted in an arbor 224 of the pallet 218 and arranged between a pair of spring supports 222.

As in the previously described embodiment, the oscillating motion of the pallet is used to drive a ratchet. The ratchet comprises a pawl 226, pivoted at 228 and biased by a spring 230. Pawl 226 drives a ratchet wheel 232 arranged on a shaft 234. A hold back pawl 236 is pivoted at 240 and held against the teeth of ratchet wheel 232 by a spring 238.

The output of the timer is derived from a gear train (not shown) via shaft 234.

As with the previous embodiment, the timing escapement speed retarding mechanism is placed in series between the input power source and the timer output shaft such that any failure will cause the output shaft to stop rather than have the possibility of it speeding up.

If still greater timing accuracy or longer time delay is desired, then a tuned, detached escapement, such as a combination of an escape wheel, lever, balance wheel and hairspring, speed control can be employed. This is illustrated in 1 FIG. 5.

The input power is supplied to an input shaft 126, by, for example, a spring powered gear and gear train (not shown). Also arranged on input shaft 126 is an escape wheel 128, the teeth of which cooperates with the pallet stones 130 of a pallet fork 132 which is pivoted at 133. The escape wheel has an intermittent clockwise rotation which counts the number of times a balance wheel 138 oscillates and also supplies to balance wheel 138 the energy it loses in friction. Escape wheel 128 advances one tooth for each complete oscillation of balance wheel 138. While letting escape wheel 128 advance, a lever 134 transmits energy to the balance wheel. Lever arm 134 is coupled to balance wheel 138 via a fork slot 136 and a balance wheel jewel 140. Balance wheel 138 has a conventional hairspring 142, therein, as shown. Restriction on the swing of the lever 134 is imposed by a pair of banking pins 144 in conventional fashion, while the open end of fork slot 136 allows jewel 140 to continue its motion allowing balance wheel 138 to rotate freely until the restoring force of hairspring 142 overcomes the motion of the balance wheel, causing it to reverse its motion. The fork slot 147 on an output lever 146 cooperating with a second balance wheel jewel 148 provides oscillatory motion to a drive pawl 150, about a pivot 152. The lever 146 is restained by a pair of output banking pins 154. The drive pawl pivots about a point 151 located on lever 146 and is held against the teeth of a ratchet wheel 158 by a spring 156. Drive pawl 150 provides intermittent motion in the direction shown to ratchet wheel 158, which is restrained from turning backward by a holdback pawl 160 pivoted at 162 and held against the teeth of ratchet wheel 158 by a spring 164. The holdback arrangement is optional.

The output of the timer is derived at an output gear train (not shown) via shaft 166 attached to the ratchet wheel 158.

As with the previous embodiments, the timing escapement speed retarding mechanism is placed in series between the input power source and the timer output shaft such that any failure will cause the output shaft to stop rather than have the possibility of it speeding up.

It will thus become obvious that any one of the very many escapements available in the prior art may be employed in the practice of the invention. The escapements illustrated herein are set forth only for illustrative purposes to show three principal classes of escapements, the two-center untuned or runaway escapement of FIG. 3, the two-center tuned" escapement of FIG. 4 and the three-center "tuned, detached" escapement illustrated by the escapement of FIG. 5.

A variation of the embodiments previously shown is to make use of a resonant rod as the oscillatory speed retarding mechanism. Again, the speed retarding mechanism is placed in series between the input power source and the time output shaft. FIG. 6 illustrates an embodiment making use of a resonant rod and, in particular, a special case thereof, the tuning fork. A highly resonant rod or tuning fork 170 is used as the speed retarding control mechanism..ln this embodiment, an input escape wheel supplies energy to a tuning fork in a similar manner as supplying energy to a balance wheel, whereby each.

complete oscillation cycle of a tuning fork advances an output ratchet wheel one tooth.

In particular, input power is applied to shaft 172 to drive escape wheel 174. Pallet fork 176 cooperating with the teeth of escape wheel 174 causes a lever 178 to oscillate about a pivot 180 between a pair of banking pins 182. Lever 178 drives one tine 188 of tuning fork 170 via a drive jewel or bearing 184, causing tine 188 to vibrate. Tuning fork 170 is fixed at 186. The vibration of tine 188 causes in like fashion the vibration of tine 190. Tine 190 is coupled to a drive pawl 192 which rotates a ratchet wheel 194. Pawl 192 is held against ratchet wheel 194 by a spring 204. The output shaft of the timer is shown at 196. A holdback pawl 198, pivoted about point 200 and spring loaded via a spring 202, may be used.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that the embodiments shown are illustrative only, and that many variations and modifications may be made without departing from the principles of the invention herein disclosed and defined by the appended claims.

lclaim 1. A fail-safe mechanical timer, comprising:

a mechanical spring driven source of rotating input power;

a driven output member; and

a speed retarding mechanism intermediate said source of input power and said driven output member and coupling said source of input power to said driven output member.

2. A fail-safe mechanical timer in accordance with claim 1, wherein said speed retarding mechanism drives said output member.

3. A fail-safe mechanical timer in accordance with claim 1, wherein said speed retarding mechanism includes an escapement mechanism.

4. A fail-safe mechanical timer in accordance with claim 3, wherein said escapement mechanism includes:

an escape drive coupled to said source of input power; and

an escape retarder coupled to said driven output member.

5. A fail-safe mechanical timer in accordance with claim 4, wherein said escape drive is an escape wheel and said escape retarder is an escapement fork.

6. A fail-safe mechanical timer in accordance with claim 5, said escapement fork having first and second pallets meshed with said escape wheel for oscillating said escapement fork, and means for transferring said oscillatory motion to unidirectionally drive said driven output member.

7. A fail-safe mechanical timer in accordance with claim 6,

wherein said transferring means includes a ratchet coupled to a balance wheel, coupled to the forked end of said input lever;

member; and an output member driven byvsaid resonant member. 7

12. A fail-safe mechanical timer in accordance with claim l 1, wherein said resonant member is a tuning fork having first and second tines.

13. A fail-safe mechanical timer in accordance with claim 12, wherein said resonant member is a tuning fork having first and second tines, said first tine being coupled to said means for supplying input power, with said driven output member being coupled to said second tine.

14. A fail-safe mechanical timer in accordance with claim 13, further including a ratchet coupled to said second tine of said tuning fork, whereby vibration of said tuning fork causes said drive member to move said ratchet unidirectionally and drive said driven member.

i l t t 

1. A fail-safe mechanical timer, comprising: a mechanical spring driven source of rotating input power; a driven output member; and a speed retarding mechanism intermediate said source of input power and said driven output member and coupling said source of input power to said driven output member.
 2. A fail-safe mechanical timer in accordance with claim 1, wherein said speed retarding mechanism drives said output member.
 3. A fail-safe mechanical timer in accordance with claim 1, wherein said speed retarding mechanism includes an escapement mechanism.
 4. A fail-safe mechanical timer in accordance with claim 3, wherein said escapement mechanism includes: an escape drive coupled to said source of input power; and an escape retarder coupled to said driven output member.
 5. A fail-safe mechanical timer in accordance with claim 4, wherein said escape drive is an escape wheel and said escape retarder is an escapement fork.
 6. A fail-safe mechanical timer in accordance with claim 5, said escapement fork having first and secoNd pallets meshed with said escape wheel for oscillating said escapement fork, and means for transferring said oscillatory motion to unidirectionally drive said driven output member.
 7. A fail-safe mechanical timer in accordance with claim 6, wherein said transferring means includes a ratchet coupled to said escapement fork and moved unidirectionally thereby.
 8. A fail-safe mechanical timer in accordance with claim 4, further including means for transferring the cyclic motion of said escape retarder to unidirectionally drive said driven output member.
 9. A fail-safe mechanical timer, comprising: means for supplying input power; an escape wheel coupled to said means for supplying power; an input lever having pallets at one end thereof and a fork at the other end thereof, said pallets being coupled to said escape wheel; a balance wheel, coupled to the forked end of said input lever; an output lever having a fork at a first end thereof, said forked end being coupled to said balance wheel; a ratchet coupled to said output lever; and an output member coupled to said ratchet.
 10. A fail-safe mechanical timer in accordance with claim 9 further including a drive member pivotally coupled to said output lever for driving said ratchet.
 11. A fail-safe mechanical timer, comprising: a resonant member; a mechanical spring driven source of rotating input power; means for supplying said input power to said resonant member; and an output member driven by said resonant member.
 12. A fail-safe mechanical timer in accordance with claim 11, wherein said resonant member is a tuning fork having first and second tines.
 13. A fail-safe mechanical timer in accordance with claim 12, wherein said resonant member is a tuning fork having first and second tines, said first tine being coupled to said means for supplying input power, with said driven output member being coupled to said second tine.
 14. A fail-safe mechanical timer in accordance with claim 13, further including a ratchet coupled to said second tine of said tuning fork, whereby vibration of said tuning fork causes said drive member to move said ratchet unidirectionally and drive said driven member. 